The invention relates to a paper sack, preferably to a valve paper sack for bulk material such as cement, gypsum, granulate, animal feed or similar, having a base, preferably a cross bottom or block bottom, and having an upper part which is disposed opposite the base and in which a valve hose is optionally arranged for filling the paper sack.
Such paper sacks are known, for example, from EP 1 858 769 B1. The typical sizes 5 kg, 10 kg or 25 kg are in particular commercially widespread. They have one or more paper layers which are formed from paper or from a paper composite and/or from coated paper.
A valve hose is optionally provided for filling such sacks which is worked into the upper part and which is placed onto a filler nozzle for filling. A fast escaping of the air during the filling process is of material significance for a fast and economic filling. On the other hand, the sack should be as leak-proof as possible after the filling. To achieve a greater product protection or a longer product stability of the filling material, a barrier layer can—as described in EP 1 858 769 B1—be placed between an inner layer and an outer layer of paper.
It has been found that a sufficient product protection cannot be ensured with the already known sacks with sensitive filling materials. Such sensitive filling materials are, for example, fast-binding products in the sector of construction materials or foodstuffs in which a loss of aroma has to be prevented.
In addition there is a demand for so-called weatherproof paper sacks whose outwardly disposed side has water-resistant or weather-resistant material properties to be able to ensure weather resistance over a specific time period. In this embodiment, it is likewise necessary to provide a sufficient venting of the paper sack during the filling process.